Abstract
Working memory impairments in dyslexia are well documented. However, research has mostly been limited to the phonological domain, a modality in which people with dyslexia have a range of problems. In this paper, 22 adult students with dyslexia and 22 age- and IQ-matched controls were presented with both verbal and visuospatial working memory tasks. Performance was compared on measures of simple span, complex span (requiring both storage and processing), and dynamic memory updating in the two domains. The dyslexic group had significantly lower spans than the controls on all the verbal tasks, both simple and complex, and also on the spatial complex span measure. Impairments remained on the complex span measures after controlling statistically for simple span performance, suggesting a central executive impairment in dyslexia. The novelty of task demands on the initial trials of the spatial updating task also proved more problematic for the dyslexic than control participants. The results are interpreted in terms of extant theories of dyslexia. The possibility of a supervisory attentional system deficit in dyslexia is also raised. It seems clear that working memory difficulties in dyslexia extend into adulthood, can affect performance in both the phonological and visuospatial modalities, and implicate central executive dysfunction, in addition to problems with storage.
Highlights
Working memory and dyslexia 3 Author Note We are grateful to Dr Viv Moore, Dr David Glasspool, and Andy Velarde for their support in producing this paper and would like to thank Prof
In order to determine whether impairments were present on the working memory span tasks after controlling for simple span, a one-way ANCOVA was performed with the composite standardised verbal working memory span scores as the dependent variable, group as the between-participants factor, and the standardised simple span composite score entered as a covariate
The results indicated that the significant group difference remained on the verbal working memory span measure after controlling for simple verbal memory span
Summary
Working memory and dyslexia 3 Author Note We are grateful to Dr Viv Moore, Dr David Glasspool, and Andy Velarde for their support in producing this paper and would like to thank Prof. Working memory and dyslexia 4 Central Executive Functioning in Developmental Dyslexia Dyslexia is the most prevalent developmental disorder, affecting some 5% of the population of the western world (Badian, 1984), despite adequate intelligence, education, and socioeconomic status It is most commonly defined as a problem with the decoding of the written word, with such processing difficulties leading to the formulation of the phonological core deficit hypothesis of dyslexia (e.g., Frith, 1985; Ramus, 2003; Ramus, Pidgeon, & Frith, 2003; Snowling, 2000; Snowling & Griffiths, 2003; Stanovich, 1988; Vellutino, 1979; Vellutino, Fletcher, Snowling, & Scanlon, 2004). It has been suggested that memory span differences between dyslexics and controls can be accounted for in terms of phonological processes, such as slow articulation rate (Avons & Hanna, 1995; Hulme, Roodenrys, Brown, & Mercer, 1995; McDougall & Donohoe, 2002) or deficits in learning, encoding, or using phonological representations (Carroll & Snowling, 2004; Kramer, Knee, & Delis, 2000; Rack, 1994; Tijms, 2004)
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